Constant On-Time Converter Stabilization Using Compensation Signal
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Solution Overview
Problem
Conventional constant on-time DC/DC converters are unstable when using ceramic capacitors with low equivalent series resistance, leading to potential sub-harmonic oscillations and instability, which prevents their use in applications requiring cost-effective and compact output capacitors.
Innovation Solution
The introduction of a compensation signal (VSLOPE) that mimics the behavior of a high equivalent series resistance, generated through a compensation circuit, to stabilize the converter operation by adjusting the switching logic based on the algebraic sum of the feedback and compensation signals, ensuring stable output voltage even with low equivalent series resistance capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ceramic capacitors with low equivalent series resistance are used, then cost and size are reduced, but converter stability deteriorates due to sub-harmonic oscillations
Solution Approach 1:
The patent introduces a compensation circuit that generates a compensation signal VSLOPE as an intermediary element. This signal mimics the stabilizing effect of high ESR capacitors by being added to the feedback signal before comparison with the reference voltage, thereby enabling the use of low-ESR ceramic capacitors while maintaining converter stability.
Solution Approach 2:
The patent changes the electrical parameters of the control system by introducing a compensation signal that dynamically adjusts the effective feedback voltage. This parameter modification allows the converter to operate stably with ceramic capacitors that would otherwise cause sub-harmonic oscillations, resolving the contradiction between cost reduction and stability maintenance.
2Volume of moving object
If ceramic capacitors with low equivalent series resistance are used, then output capacitor size is reduced, but converter stability deteriorates due to sub-harmonic oscillations
Solution Approach 1:
The compensation circuit generates a compensation signal VSLOPE that acts as an intermediary to replicate the stabilizing function of high ESR. This signal is added to the feedback voltage before comparison, enabling the use of compact ceramic capacitors while preventing sub-harmonic oscillations and maintaining converter stability.
Solution Approach 2:
By introducing the compensation signal that dynamically modifies the feedback voltage parameter, the system achieves stable operation with low-ESR ceramic capacitors. This parameter change enables the use of smaller output capacitors without sacrificing converter stability.
3Reliability
If high equivalent series resistance capacitors are used, then converter stability is improved, but cost and size increase
Solution Approach 1:
The patent introduces a compensation circuit that generates a compensation signal VSLOPE to mimic the stabilizing effect of high ESR capacitors. This intermediary signal is added to the feedback signal before comparison with the reference voltage, enabling the use of low-ESR ceramic capacitors while maintaining the stability benefits of high ESR capacitors, thereby reducing cost.
4Reliability
If high equivalent series resistance capacitors are used, then converter stability is improved, but output capacitor size increases
Solution Approach 1:
The compensation circuit generates a compensation signal VSLOPE that serves as an intermediary to replicate the stabilizing function of high ESR capacitors. This signal is added to the feedback voltage before comparison, enabling the use of compact ceramic capacitors while preventing sub-harmonic oscillations, thereby maintaining stability without increasing capacitor size.
Data Source
AI summary
The present invention discloses a control circuit for constant on-time converter and a control method thereof. The proposed constant on-time DC/DC converter stabilizes the system and improves the performance of the load transient response without large equivalent series resistance of the output capacitor.